The present invention pertains to a sheet element that can be used for the formation of bags, which are suitable for packing and for preserving food products under vacuum as well as not under vacuum.
Bags for the above-mentioned use, which are produced starting from at least one flat sheet folded onto itself and/or cut out and sealed in a suitable manner to form a container closed on three sides and having an open mouth which can be closed by means of sealing after having inserted the desired product therein, have already become known from the state of the art.
The starting sheet usually consists of at least two layers or films made of materials which are different, usually transparent, intimately combined with one another on the inside surface by means of any technically available system, such as coextrusion, lamination, stratification for successive extrusions, etc.
At least one of these layers, the outer layer in case of only two layers or the outer or middle layer in the case of three or more layers, consists of a thermoplastic material that is compatible for contact with foods and is impermeable to gases, such as: polyamide, polyester (properly treated), ethyl vinyl alcohol or any other material suitable for the object that may be technically available.
The object of this layer is to prevent the penetration inside the bag of oxygen, which proves to be the main cause of the perishability of many foods.
However, the inside layer consists of a thermoplastic material that is likewise compatible for contact with foods and can be readily heat-sealed, such as polyethylene, polypropylene, ethyl vinyl acetate or any other material suitable for the object that may be technically available.
Any other layers always only consist of thermoplastic materials that are compatible for their contact with foods and have the function of binding among the various layers of different material in order to improve their joining or they have protective functions.
Also well known from the state of the art are bags in which the inside layer of at least one of its sides is provided with channels in order to promote the outlet of air when applying the vacuum to the package and closing it. According to one embodiment such channels are obtained by means of a pressure deformation of the starting material, especially with an embossing operation, by means of which a network of channels crossed and separated by protuberances or islands is formed.
Such a network of channels promotes the evacuation of air but has the drawbacks of having a process for its production that is burdensome and very delicate in the setup phase (a compression force that is too high may lead to damage of the film, while a force that is too low may not produce the permanent deformation that creates the channels for the evacuation of the air).
Moreover, the resulting product has the defect that, in the presence of heat, the sheet tends to recover its original flat shape, and the channels tend to disappear. This implies that in the use that is provided with the suction machines corresponding to the sealing bar of the heat-sealing unit the heat of the previous sealing operations makes the channels for an evacuation of the air disappear, making the product unusable, unless one waits for the complete cooling off which involves a useless loss of time. Moreover, a difficulty was found in ensuring the tightness of the seal in the presence of folds on the smooth sheet.
According to another embodiment, filiform, parallel protuberances are provided on the inner surface of at least one side of the bag, which extend longitudinally from the mouth to the bottom of the bag. This results in the formation of parallel channels, which, however, do not communicate with one another crosswise. This represents a drawback since, if for any reason, not all the channels communicate with the generator of the vacuum at the time of closing, air pockets may remain in the bag, compromising the preservation of the packaged product.
For the reason described above, the bag may thus have a maximum width that is equal to the opening mouth of the suction and sealing unit.
Moreover, the production process is very delicate in the setup phase, and filiform elements, which are obtained by coextrusion in order to be able to be readily sealed, must have highly reduced dimensions, with the result of being uncontrollable both in terms of shape and in terms of size, and therefore, the effectiveness of the parallel channels that they produce may be extremely variable. In addition, the channels that are to be created are air spaces between the protuberances and the upper sheet, which, being flexible, may definitely adhere to the protuberance, considerably reducing the air space blocking the evacuation of air.
This occurs exactly in the zone in which the suction is exerted, where a seal made of elastic material is present (which is necessary for the holding of the vacuum during the operation proper), which tends to make the two sheets adhere.
Starting from these premises, the primary object of the present invention is to provide a material for bags for the vacuum-packing of products, which, due to its shape and configuration, is produced in a simpler and a more functional manner from the embossed and from the material with channels that run longitudinally from the mouth to the bottom of the bag, and which is able to ensure a complete discharge of the air under all conditions at the time of creating the vacuum and of closing the container.
This object is accomplished, according to the present invention, with a sheet element for the formation of a bag for the vacuum-packing of products, wherein the element has at least two layers or films of different material that are joined together and where the layer or film intended to form the inner surface of at least one side of each bag has channels, which are obtained by means of ribs, which are oriented diagonally with respect to the longitudinal axis of the bag, and each is provided with a plurality of transverse cavities or notches, which are spaced along the rib proper. Thus, in each bag, the diagonal ribs delimit the channels which converge at a non-90xc2x0 angle at the mouth of the bag, and the transverse cavities or notches on the ribs put the channels into a lateral communication with one another, all of which is to make possible a complete evacuation of air from the bag when the vacuum is applied. Actually, even the channels that should then not communicate directly with the source of the vacuum applied to the mouth of the bag, would, however, hereby be connected indirectly by means of the cavities or notches on the ribs.
These projections or ribs may be parallel to one another or crossed and each produced with one or more parallel grooves, having the same function as the above-mentioned channels. These are made of a thermoplastic material having the same characteristics as the material forming the inner layer of the sheet, and therefore, suitable for contact with foods and readily sealable.
Moreover, the ribs represent additional material (support material), which is an advantage for the effectiveness of the sealing by blocking any folds that should form in the individual sheets.
Further details of the present invention shall become evident from the description provided below with reference to the attached simplified drawings.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated.